In general, a hydraulic master cylinder assembly, such as for a clutch or a brake, includes a cylinder body with a bore that slidably receives a piston, and an actuating mechanism to effect axial movement thereof in response to operation of the actuating mechanism, to deliver a hydraulic operating force. In a brake master cylinder, such as for a motorcycle, the actuating mechanism generally includes a hand-operated lever mounted on the handlebar of the motorcycle, with the lever biased away from the handle in its rest position. The motorcyclist grips the handle along with the lever and closes his/her hand to move the lever toward the handle. The lever is typically operably coupled to the piston, such that the manner of movement of the lever, in terms of how far the lever is moved (i.e., the lever stroke), how rapidly the motorcyclist moves the lever through a stroke, and so forth, often determines the nature of the hydraulic operating force and the response of the brake thereto.
Motorcyclists often desire to adjust characteristics of the brake levers, such as to more comfortably accommodate the motorcyclist's hand size, for example by moving the at-rest position of the lever relative to the handle, to exhibit a desired amount of resistance against being pulled toward the handle, for example by changing the mechanical advantage of the lever, and so forth. In general, such characteristics are adjusted by a mechanic when the motorcycle is not being ridden.
Motorcyclists also often desire to adjust the responsiveness of their brakes to operation of the brake levers. This is sometimes accomplished by choosing a master cylinder of a particular size, which is often described in terms of the diameter of the bore in which the piston operates. Manufacturers offer a range of master cylinders having differing bore diameters, for example to suit variations among motorcycles, such as hydraulic system capacity, vehicle weight, brake type, brake pedal ratio, and so forth. Such cylinders are usually offered in a range of standard bore sizes. However, in some applications, such as in motorcycle racing, a racing team may utilize a number of cylinders of different sizes for a single motorcycle, such as to accommodate different circuits, different weather conditions, and variations in rider technique. Changing a master cylinder, however, requires significant time and careful effort, and in general is an operation that cannot be performed when the motorcycle is in use.